Friday, March 24, 2017

Jon Erdman
Published: March 24,2017
Two more rounds of rain and
mountain snow are on the way to California through this weekend due to a
pattern change that began at the start of this week. This has ended a
more than two-week respite from one of the wettest winters on record in the Golden State.(MORE: 5 Reasons March Weather Is Frustrating)
An upper-level ridge of high pressure that was responsible for the mainly dry and warm conditions in the West has broken down.
In
its place, multiple southward dips in the jet stream, or troughs, are
now steering the storm track back toward California through this
weekend.

Two More Rounds

The first Pacific cold front and its associated jet stream dip pivoted into the West Coast Monday through Wednesday.
Roadway flooding was reported in the Sacramento area on Tuesday, and funnel clouds were spotted near Turlock.
A severe thunderstorm caused wind damage in Twain Harte, which is
located southeast of Sacramento in the Sierra Nevada foothills.

Current Radar, Temperatures, Conditions

(MAPS: 7-Day Rain/Snow Forecast)
Another
Pacific front will came ashore Friday, and continues eastward into the
Great Basin and Rockies. That storm will be accompanied by another burst
of moderate to locally heavy rainfall, mountain snow and gusty winds.
This area of low pressure will go on to become another wave of severe weather Sunday and Monday in the Plains and South
Behind
that system, another cold front will sweep into the Northwest Sunday
and its moisture will also extend southward into the northern half of
California.

The Second System Late This Week

How Much Rain, Mountain Snow?

The
good news is that none of these storms appear to be as strong or
slow-moving as some of the atmospheric river events that occurred in
January and February.

Rainfall Outlook

The additional
storms will bring the heaviest rain to the coastal ranges of northern
California, southern Oregon and the Sierra foothills below snow level,
where 1 to 2 inches of additional rainfall is likely.
Other low elevations of northern California could total an inch of rain through this weekend, including the Bay Area and Sacramento.
(FORECAST: Los Angeles | San Diego)
Some
mudslides, rockslides and debris flows are possible in spots with each
round, given the already saturated ground from this winter.

Rain and Snow Outlook Through Sunday

Snowfall Outlook

The
combination of all these systems will bring 6-18 inches of snow to the
Sierra through early next week. Snow and gusty winds are likely to
affect travel through Sierra passes into Saturday morning, as up to one
foot of snow is expected.(MORE: Where March and April Are the Snowiest Months)
Over a foot of snow is also possible in the Cascades, Siskiyous and parts of the Rockies.
This is the first decent snow event in South Lake Tahoe, California, since March 5.

Adding to an Impressive Spring Snowpack

By late-March standards, the water content estimated in the Western snowpack is the highest in several decades.
According to the National Resources Conservation Service SNOTEL network,
Leavitt Lake, at an elevation of 9,604 feet in the central Sierra south
of Lake Tahoe, was estimated to have a snowpack of just under 20 feet:
234 inches.
The estimated water equivalent of that snowpack – just
over 100 inches – was easily the highest snow-water content for any
March 19 on record in their database dating to 1989.
Water content in the Wasatch and northern Rockies also was generally at least 33 percent above average for this time of year.

Estimated snow-water content percent of average for March 20, 2017, in western U.S. river basins.

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